Ultrasonic grinding apparatus



March 15, 1966 RONEY 3,239,965

ULTRASONIC GRINDING APPARATUS Filed Sept. 13, 1961 6 Sheets-Sheet 1 IN VEN TOR.

,4 TTORNE Y,

March 15, 1966 N. RQN'EY 3,239,965

ULTRAS ONIC GRINDING APPARATUS Arron/vs Y.

March 15, 1966 RONEY 3,239,965

ULTRASONIC GRINDING APPARATUS Filed Sept. 15, 1961 6 Sheets-Sheet 5 on N Q IE S INVENTOR.

ATTOR EY.

March 15, 1966 Filed Sept. 13, 1961 R. N. RONEY ULTRAS ONIG GRINDING APPARATUS 6 Sheets-Sheet 5 INVENTOR.

A TTORNEY March 15, 1966 R. N. RONEY 3,239,965

ULTRASONIC GRINDING APPARATUS Filed Sept. 13, 1961 6 Sheets-Sheet 6 INVENTOR ATT EY.

United States Patent 3,239,965 ULTRASONIC GRINDING APPARATUS Richard N. Roney, Dayton, Ohio, assignor to The Sheffield Corporation, Dayton, Ohio, a corporation of Delaware Filed Sept. 13, 1961, Ser. No. 138,243 13 Claims. (Cl. 51-92) This invention relates to grinding and more particularly to grinding in which an ultrasonic vibration is applied to the grinding wheel.

Prior art attempts at ultrasonic grinding have not been satisfactory because they have attempted to induce radial vibratory motions to the grinding wheel by employing magnetostrictive material embedded in the abrasive disc as in the Comstock 2,695,478. Such an arrangement is not satisfactory in the production of uniform vibratory movements of the wheel periphery and involves a very costly construction.

One object of the present invention, therefore, is to provide a new and improved arrangement for inducing uniform radial vibrations to grinding wheels.

Another object is the provision of a new and improved structure of this character, simple in construction and capable of using existing grinding wheels.

A still further object of the invention is the provision of new and improved structure of the character mentioned whereby the grinding wheel, of commercial character, can be simply and quickly applied and replaced.

Another object is a provision of a new and improved structure whereby axial vibrations are applied to a grinding wheel hub and these are converted into radial vibrations applied to a radial hub flange to which the inside of the abrasive disc is secured.

A further object is the provision in a grinding apparatus having an ultrasonically vibrating grinding Wheel, of new and improved supporting and bearing structure so that the grinding wheel may be rotated at satisfactory grinding speeds.

Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.

In the drawings;

FIG. 1 is a perspective view of the upper portion of a grinding machine embodying the principles of the present invention,

FIG. 2 is a longitudinal central section of the grinding wheel driving head shown in FIG. 1,

FIG. 3 is a cross-sectional view of the grinding wheel structure that is driven by the grinding head,

FIG. 4 is a cross-sectional view taken on the line 44 of FIG. 2,

FIG. 5 is a cross-sectional view taken on the line 5-5 of FIG. 2,

FIG. 6 is a cross-sectional view taken on the line 6-6 of FIG. 2,

FIG. 7 is a diagram identifying various dimensions used in the following description,

FIG. 8 is a cross-sectional view of a modified grinding wheel hub, and

FIG. 9 is a central sectional view of another modification of the grinding wheel hub.

In accordance with the present invention applicant has provided a vibration producing driving head which is rotated about its central axis and supported by a bearing structure so arranged as to adequately support a high speed grinding wheel such that the vibrations induced in the grinding wheel can be withstood. This vibration producing driving head is connected to a grinding wheel hub which in turn is connected to the abrasive disc that makes up the outer portion of the grinding assembly. In the grinding wheel hub axial high speed oscillations preferably 3,239,965 Patented Mar. 15, 1966 of the order of 20,000 cycles per second are transformed into radial vibrations which travel out away from the axis of rotation and impart high speed vibratory motion to the wheel periphery. It has been found that when high speed vibration is applied to the active surface of the grinding wheel the rate of cutting is very considerably increased without burning or injuring the material operated on and with a further result of a reduction in the wear that takes place on the grinding wheel itself. Hard to machine materials can be much more readily cut in this way.

The ultrasonic grinding machine shown in FIG. 1 generally comprises a base having an upright 10 which is provided with suitable guide ways on which the head structure 12 of the machine is mounted for vertical movement. The head structure 12 is raised and lowered along the guide ways in any conventional manner by rotating the hand wheel 14. The carriage or work table 16 is mounted for longitudinal movement by means of conventional slide mechanism and the longitudinally movable slide mechanism in turn is mounted on cross or transverse ways 18 for movement towards and away from the upright 10. Such an arrangement of the table and head structure insofar as its support and movements is concerned may be that of a Brown and Sharp Universal Surface Grinder. The workpiece W is fixed on the work table and if desired the workpiece itself may be ultrasonically vibrated by mounting it on the end of a vertically supported transducer T carried by the work table 16 with the workpiece W bonded to the end of the transducer. However, in general the workpiece may be mounted in fixed position on the work table itself.

The embodiment shown in FIGS. 1 thru 6 of the drawing comprises a grinding wheel unit G and a driving unit D which both induces vibration in and rotatably drives and supports the grinding wheel unit G. The driving unit D, as shown, comprises a driving hub structure 20 which rotates about its longitudinal axis 22. The length of this hub structure is such that when connected with the grind ing wheel structure and a transducer T the outer end 26 of the hub structure 20 will be axially vibrated at an antinodal region at a rate of approximately 20,000 cycles per second. The inner end of the hub structure as indicated at 24 is fixed to the ultrasonic transducer T which may be of any suitable construction for example as generally illustrated in the patent to Carwile 2,651,148.

Ultrasonic vibrations, of course, tend to be damaging to bearing structures. In accordance with the present invention a radial supporting flange 28 is provided on the hub structure 20 at a position substantially corresponding to an axial nodal region. generally that compression in one direction produces an expansion at right angles and the degree to which this is accomplished has been termed Poissons Ratio. Since the flange 28 is located at an axial node there is substantially no axial movement but there are radial vibrations produced in the flange as a result of the axial vibration of the transducer. This flange 28 is attached at one side thereof to a carrying structure and this attachment is made at the location of a radial nodal zone. This attachment is to a bearing ring 32, a series of spaced attaching screws 36 securing the parts together but with a ring of vibration insulating material 34 positioned between the bearing ring 32 and the flange 28. Attachment in this manner miniinizes the amount of vibratory movement imparted to the bearing ring 32.

The periphery of the bearing ring 32 is provided with a radial groove 38, the radially inner surface 40 of which provides a journalling surface by which the bearing ring 32 is supported for rotation. The radially inner surface 40 is rotatably mounted in a split bearing structure 44, the inner half 46 of which is rigidly mounted on the head It is a property of materials structure 12. The outer half 48 of the bearing struc ture 44 as shown in FIG. 4 is secured in place by means of machine screws 50. Inasmuch as some heat may be developed in the bearing structure, cooling liquid is preferably supplied to the inlet 52 and flows through drilled passages 54, 56, 58 and 60 to an outlet connection 62. Suitable O-rings 64 are provided at the juncture of the drilled passages in the inner and outer sections of the bearing structure 44 and form a seal against loss of liquid.

The bearing ring 32 is adapted to be rotatably driven by means of a generally tubular structure 66 surrounding the transducer T and the opposite end of this tubular structure is supported by a suitable pillow block 68. The tubular structure 66 has a closed end 70 to which a bearing hub 72 is secured by means of machine screws 74. The bearing hub 72 has an outer reduced diameter which is journaled in the sleeve bearing 78 of the pillow block 68. A suitable shoulder 80 is provided inwardly of the sleeve 78 and a suitable bearing washer 82 is arranged therebetween to limit movement in an axial direction. Axial movement in the opposite direction is limited by a collar 84 which is fixed to the outer end of the hub structure 76 with a bearing washer 86 arranged between the collar and the pillow block structure. The bearing hub 72 has a somewhat larger diameter portion 90 inwardly of a pillow block 68 and the unit is rotatably driven by a pulley 92 which is arranged over the section 90 of the bearing hub and is suitably bolted against the sides of a radial shoulder 94 as shown in FIG. 2. The outer periphery of the bearing hub 72 is reduced in diameter between the pulley 92 and the point where it joins a tubular structure 76. A pair of slip rings 96 and 98 are embedded in rings of insulating material 100 held within a reduced diameter section 102 of the pulley 92. These slip rings supply electrical energy to the transducer T The transducer T is provided with flat laminations 104 of magnetostrictive material, brazed to the end surface 24 of the hub structure 20. An axially extending slot 106 is provided centrally in the laminations which are clamped together by clamping members 110 and held together by through bolts 108. An insulated wire 112 extends from the slip ring 96 through the bearing hub 72 and is wound around the laminations 104. The wire crosses over and is wound on the other side of the laminations and then passes through the hub structure 72 to make contact with the other slip ring 98. The slip rings are energized through brushes 114 and 116 which in turn are connected to the wires 118 and 120 leading to a suitable external source of alternating current.

In accordance with the present invention uniform radial vibrations can be generated in the grinding wheel by means of axial vibrations applied to one end of the grinding wheel hub. One preferred structure for achieving this object, as shown most clearly in FIG. 3, embodys a ring A of abrasive material bonded to the periphery of the grinding wheel hub structure 122. The hub structure 122 in turn is removably aflixed to the end surface 26 of the driving hub 20. The hub 122 is provided integrally with a radially extending flange 124 and the axial length and size of the hub structure 122 is such that flange 124 is arranged at an axial nodal position along the length of the hub. Radial vibrations are thus produced in and transmitted outwardly through the radial flange 124 to the abrasive ring.

In order that vibrations will be effectively transmitted from the metallic portion of the flange 124 to the abrasive disc A, the mechanical impedance of the abrasive material A should preferably generally match the mechanical impedance of the metallic hub structure. This is accomplished by making the mechanical impedance Z of the wheel hub equal to the mechanical impedance Z of the annular abrasive disc as given by the following equations and as illustrated in FIG. 7 of the drawings:

Where:

X =Radius of an imaginary flange having a radial period of vibration matching the axial period of vibration in the hub.

X =Radius of a grinding wheel including abrasive material having a period of vibration matching the hub.

A =Peripheral area of hub of desired grinding wheel.

A =Peripheral area of grinding wheel.

Y Youngs modulus of hub material.

Y =Youngs modulus of abrasive material.

C =Velocity of sound in hub material.

C =Velocity of sound in abrasive material.

W =Angular frequency of vibration of the imaginary transducer-wheel hub system (Zn-f) of a single hub material.

W =Angular frequency of vibration of the desired composite grinding wheel (21rf).

X =Change in radius that must occur in X (imaginary wheel hub radius) to provide a radial thickness of abrasive material X (X :X (X -X which will make Z =Z By making the mechanical impedance of the abrasive ring substantially equal to the mechanical impedance of the hub at the point of juncture, a maximum of vibration is transmitted through the juncture, a minimum of reflected waves is produced off of the point of juncture, and a minimum of damaging impact is exerted upon the ring of abrasive material. While it is not necessary that the period of vibration of the composite radial flange of the grinding wheel be equal to the period of vibration for its axial hub structure; definite advantages occur by designing the composite radial flange structure to be in tune with the hub structure. One such advantage comes about by reason of the fact that by so doing a desired amplitude of vibration can be achieved in the periphery of the grinding wheel with a minimum of driving energy.

Applicant has further found that it is quite diflicult to get a satisfactory bond between the abrasive material and the metallic hub structure even when the impedances of the abrasive material and hub structure are matched. Any suitable strong bonding material can be used to create the bond, as for example, a low temperature curing epoxy resin which sets up at a temperature not exceeding F. Applicant has found that when resins having higher setting temperatures are used, suflicient shrinking of the metallic hub occurs after curing takes place to produce a failure of the bond. Applicant has further found that where the periphery of the hub structure upon which the annular abrasive disc A is attached or bonded is a cylindrical surface, it is extremely diflicult if not impossible, to obtain a satisfactory bond; inasmuch as the bonding material is wiped off of the surfaces when they are telescoped together. To avoid this considerable clearance must be provided, which clearance necessitates a considerable thickness of bonding material which considerably dampens and reduces the amount of vibration which is transmitted across the bond. In applicants preferred embodiment, the mating surfaces of the abrasive wheel A and outer periphery of the hub structure 124 are matching tapers. By making the juncture occur on tapered surfaces, the bonding material that is applied to each of the surfaces before assembly is not wiped off of the surfaces, but instead is forced into the pores of the abrasive material A. Further benefit is achieved in that it is possible to squeeze out most of the bonding material, so that the grains of the abrasive material A bear directly against the external surface of the hub flange 124 to efficiently transfer vibration from the metallic flange 124 to the abrasive material. The angle at which the taper is made is not particularly critical so long as a suflicient taper is provided to prevent the bonding material from being wiped off of the surfaces; and it has been found that an angle of approximately degrees is entirely satisfactory. It has further been found that a roughened peripheral surface on the flange 124 is desirable in that it allows direct bearing of the abrasive material on portions of the metallic flange 124, and at the same time increases the area of bonding surface so that a better bond is produced.

In some instances, a satisfactory support will be provided for the grinding wheel G by the bearings 46 and 68, so that the outboard bearing 126 shown in FIG. 3 will not be necessary. In order that an additional support can be provided for the grinding wheel G in such a manner that the vibrations of the hub structure 122 will not damage the bearing, an axially extending bore 128 is provided in the end of the hub structure opposite the driving unit D, so that a bearing support is provided in the region of the axial node of hub 122. An annular nylon ring bearing 130 is positioned in the inner end of the bore 128 directly beneath the flange 124, and the nylon ring bearing 130 is in turn supported on the inner end of a stationary shaft 132 which extends in through the bore 128. The nylon bearing 130 is held against axial movement by a suitable shoulder 134 provided on the stationary shaft 132, and the bottom end of the bore 128. The stationary shaft 132 may be held in any suitable manner, and as shown in the drawing is provided with a radial flange 136 which is in turn suitably bolted to a stationary support 138 that is welded to the head structure 12.

While the structure of FIGS. 1 through 6 shows one embodiment of the invention, it will be possible in some instances to provide a hub structure for the grinding wheel which does not extend substantially beyond the grinding wheel and in which an outboard hearing may not be provided. In such instances, it will still be preferable to design the mechanical impedance of the abrasive ring so that it generally matches that of the hub structure and to bond the abrasive ring to the hub structure by means of a tapered surface, as previously explained.

Thus, in the construction shown in FIG. 8 a driving hub 20 may be provided and driven in the same manner as shown in FIG. 2. This hub is attached to a metallic grinding wheel hub 144 having an inner hub portion 145 and an outer integral ring 146 with a space 147 therebetween. The total cross sectional area of the outer ring portion 146 of the hub is substantially the same as the inner hub portion 145 and the provision of the slot 147 locates the general plane of the grinding wheel substantially at an axial nodal region along the hub. Thus the axial vibrations transmitted to and through the hub are converted into radial oscillations, the nodal point being indicated at 148. Steel, Monel metal or beryllium copper or other suitable material may be used in the construction of the grinding wheel hub in this and in the other modifications of the invention.

As shown in FIG. 9, the driving hub 20 may be connected to a grinding wheel hub 150, axial ultrasonic vibrations transmitted to the end portion 151 of the grinding wheel hub being transmitted outwardly and radially into radial vibrations due to the outward flare shown at 152. The grinding Wheel hub is so designed that the axial node occurs at a point 153 which lies substantially in the plane that contains the grinding wheel disc 154. In this construction, the grinding wheel itself may be bonded directly to the outwardly extending portion 155 of the grinding wheel hub in the same manner as illustrated in FIG. 3. However, as shown in FIG. 9, the abrasive ring is shown bonded to a separate metallic annular ring 156 along the bond line 157 which is an til annular surface extending at an angle of the order of 10 degrees out of parallelism with the longitudinal axis of the grinding wheel hub. This bond is effected in the same manner as has been previously described. The ring 156 is a metal ring with a slight taper fitting the taper of the grinding Wheel hub and is held securely on the hub by a holding ring 158 secured by bolts 159 so that a secure and tight but removable fit is obtained between the ring 156 and the grinding Wheel hub. The composite abrasive disc and metal ring 156 may be made as a unit by the grinding wheel manufacturer, either with an epoxy resin bond or with an integral bond provided in the manufacturing of the grinding wheel itself so that different grinding Wheels can be conveniently and readily attached to the outer portion of the grinding wheel hub.

It will be apparent that the objects previously enumerated, as well as others, have been accomplished and that a radially vibrating grinding wheel has been provided which is simple in design and capable of being quickly and removably attached to a rotatable driving unit, with an efiicient transformation of axial ultrasonic vibrations into uniform radial vibrations occurring at the working face of the grinding disc.

It is to be understood that the invention is not limited to the particular construction shown and described and it is intended that the invention shall cover all novel adaptations, modifications and arrangements thereof which come within the scope of the following claims:

What is claimed is:

1. In a grinding machine, an abrasive disc, a metallic driving hub to which said abrasive disc is fixed, means for rotating said hub at grinding speed and means for imparting ultrasonic vibrations in an axial direction to said hub, the radial plane of the disc having a location substantially corresponding to 'an axial nodal zone of the hub so that axial vibrations of the hub produce radial vibrations at the periphery of the disc.

2. In a grinding machine, an abrasive disc, a metallic driving hub having a peripheral flange to which said abrasive disc is fixed, means for rotating said hub at grinding speed and means for imparting ultra-sonic vibrations in an axial direction to said hub, the radial plane of the peripheral flange and disc having a location substantially corresponding to an axial nodal zone of the hub so that axial vibrations of the hub produce radial vibrations at the periphery of the disc.

3. In a grinding machine, an abrasive disc having a frustoconical inside surface, a metallic driving hub having a frustoconical outer surface bonded to the frustoconical inner surface of the disc, means for rotating said hub at grinding speed and means for imparting ultrasonic vibrations in an axial direction to said hub, the radial plane of the disc having a location substantially corresponding to an axial nodal zone of the hub so that axial vibrations of the hub produce radial vibrations at the periphery of the disc.

4. In a grinding machine: an axially extending hub structure having an end surface and a radially extending flange portion spaced from said end surface, a grinding wheel fixed to said hub structure, means inducing ultrasonic vibrations on said end of said hub at a generally fixed frequency to create an axial nodal region at a predetermined distance from said end surface, said radially extending flange portion being positioned generally at said axial nodal region, an annular bearing ring fastened to one side of said radial flange, bearing means rotatably supporting said annular bearing ring, and means for rot-atably driving said hub structure for rotation on said bearing means.

5. In a grinding machine: an axially extending hub structure having an end surface and a radially extending flange portion spaced from said end surface, a grinding wheel fixed to said hub structure, means inducing ultrasonic vibration on said end of said hub at a generally fixed frequency to create an axial nodal region at a predetermined distance from said end surface, said radially extending flange portion being positioned generally at said axial nodal region and said flange having a radial nodal region ardially inwardly from its outer periphery, an annular bearing ring at one side of said flange, means generally located at said radial nodal region securing said bearing ring to said flange, bearing means rotatably supporting said annular bearing ring, and means for rotatably driving said hub structure for rotation on said bearing means.

6. In a grinding machine: an axially extending driving hub structure having an end surface and a radially extending flange portion spaced from said end surface, means inducing ultrasonic Vibration on said end of said hub at a generally fixed frequency to create an axial nodal region at a predetermined distance from said end surface, said radially extending flange portion being located generally at said axial nodal region, an annular bearing ring fastened to one side of said radial flange, bear-ing means rotatably supporting said annular hearing ring, means for rotatably driving said driving hub structure for rotation on said bearing means, an axially extending grinding wheel hub having a first end surface removably affixed in vibration transmitting engagement with an end of said driving hub, said grinding wheel hub having a radially extending flange portion located at an axial nodal Zone in such manner that radial vibration is induced in said flange, and an annular ring of brasive material bonded to the periphery of said radial flange.

7. In a grinding machine: an axially extending driving hub structure having an end surface and a radially extending flange portion spaced from said end surface, means inducing vibration on said end of said hub at a generally fixed ultrasonic frequency to create an axial nodal region at a predetermined distance from said end surface, said radially extending flange portion being located generally at said axial nodal region, an annular bearing ring fastened to one side of said radial flange, bearing means rotatably supporting said annular bearing ring, means for rotatably driving said driving hub structure for rotation on said bearing means, an axially extending grinding wheel hub having a first end surface removably aflixed in vibration transmitting engagement with an end of said driving hub, said grinding Wheel hub having a radially extending flange portion located at an axial nodal zone in such manner that radial vibration is induced in said flange, and an annular ring of abrasive material bonded to the periphery of said radial flange, said periphery and inner surface of said annular ring having matching tapered surfaces, whereby a light vibration transmitting juncture is produced.

8. In a grinding machine: an axially extending driving hub structure, means inducing ultrasonic axial vibration on said hub at a generally fixed frequency, means rotatably journalling said driving hub structure, means for rotatably driving said driving hub structure for rotation on said journalling means, an axially extending grinding wheel hub having a first end surface removably aflixed in vibration transmitting engagement with an end of said driving hub, said grinding Wheel hub having a radially extending flange portion spaced from said first end surface at an axial nodal region so that radial vibration is induced in said flange, an annular of abrasive material bonded to the periphery of said radial flange, said grinding wheel hub having an axially extending opening extending from the opposite end of said grinding wheel hub to a region beneath said radially extending flange, and means extending into said opening and rotatably supporting said grinding wheel hub generally radially inwardly of said flange.

9. In a grinding machine: an axially extending driving hub structure having an end surface and a radially extending flange portion spaced from said end surface, means inducing ultrasonic axial vibration on said end of said hub at a generally fixed frequency to create an axial nodal region at a predetermined distance from said end surface, said radially extending flange portion being positioned generally at said axial nodal region, means rotatably journalling said driving hub structure by means of said radial flange, means for rotatably driving said driving hub structure for rotation on said journalling means, an axially extending grinding wheel hub having a first end surface re movably aflixed in vibration transmitting engagement with an end of said driving hub, said grinding wheel hub having a radially extending flange portion spaced from said first end surface at an axial nodal region so that radial vibration is induced in said flange, an annular ring of abrasive material bonded to the periphery of said radial flange, said grinding Wheel hub having an axially extending opening extending from the opposite end of said grinding wheel hub to a region beneath said radially extending flange, and means extending into said opening and rotatably supporting said grinding wheel hub generally radially inwardly of said flange.

10. A grinding wheel for attachment to a rotatable ultrasonically vibratory structure and having a peripheral surface that vibrates radially at high frequency generally in the ultrasonic range and comprising: an axially extending metal hub structure having an end surface for tight vibration transmitting engagement with said rotatable structure, said hub structure having an integral radially extending flange portion spaced from said end surface of said hub structure at an axial nodal region so that radial vibration is induced in said flange at said frequency, and an annular ring of abrasive material bonded to the periphery of said integral flange, said flange periphery and inner surface of said annular ring having matching tapered surfaces, whereby a tight vibration transmitting juncture is produced.

11. A grinding wheel for attachment to a rotatable ultrasonically vibratory structure and having a peripheral surface that vibrates radially at a generally predetermined ultrasonic frequency and comprising: an axially extending hub structure having an end surface for tight vibration transmitting engagement with said rotatable structure, said hub structure having a radially extending flange portion spaced from said end surface of said hub structure at an axial nodal region so that radial vibration is induced in said flange at said predetermined frequency, and an annular ring of abrasive material bonded to the periphery of said flange, said annular ring having a mechanical impedance at said frequency which is generally equal to the mechanical impedance of said hub.

12. A grinding wheel for attachment to a rotatable ultrasonically vibratory structure and having a peripheral surface that vibrates radially at a generally predetermined frequency and comprising: an axially extending hub structure having an end surface for tight vibration transmitting engagement with said rotatable structure, said hub structure having an integral radially extending flange portion spaced from said end surface of said hub structure in such manner that radial vibration is induced in said flange at said predetermined frequency, and an annular ring of abrasive material bonded to the periphery of said integral flange, said periphery and inner surface of said annular ring having matching tapered surfaces, whereby a tight vibration transmitting juncture is produced, and said annular ring having a mechanical impedance which is substantially equal to the mechanical impedance of said hub.

13. A grinding wheel for attachment to a rotatable ultrasonically vibratory structure and having a peripheral surface that vibrates radially at a generally predetermined frequency and comprising: an axially extending hub structure having an end surface for tight vibration transmitting engagement with said rotatable structure, said.

hub structure having an integral radially extending flange portion spaced from said end surface of said hub structure in such manner that radial vibration is induced in said flange at said predetermined frequency, an annular ring of abrasive material bonded to the periphery of said integral flange, said hub having an axially extending opening extending from the opposite end of said hub structure to beneath said radially extending flange, and means for rotatably supporting said hub structure in said opening generally radially inwardly of said radially extending flange. 10

References Cited by the Examiner UNITED STATES PATENTS 2,651,148 9/1953 Carwile 51-59 2,695,478 11/1954 Comstock et a1. 51-59 3,015,914 1/1962 Roney 51--59 ROBERT C. RIORDON, Primary Examiner.

FRANK H. BRONAUGH, FRANK E. BAILEY,

Examiners. 

1. IN A GRINDING MACHINE, AN ABRASIVE DISC, A METALLIC DRIVING HUB TO WHICH SAID ABRASIVE DISC IS FIXED, MEANS FOR ROTATING SAID HUB AT GRINDING SPEED AND MEANS FOR IMPARTING ULTRASONIC VIBRATIONS IN AN AXIAL DIRECTION TO SAID HUB, THE RADIAL PLANE OF THE DISC HAVING A LOCATION SUBSTANTIALLY CORRESPONDING TO AN AXIAL NODAL ZONE OF THE HUB SO THAT AXIAL VIBRATIONS OF THE HUB PRODUCE RADIAL VIBRATIONS AT THE PERIPHERY OF THE DISC. 